1. Field of Use
This invention relates generally to a blast hole drilling rig and especially to a control system for a modulatable power transmission system which drives the rotary drill holder thereof. In particular, it relates to such a control system which includes an improved manually operable electromechanical drill control unit having mechanically interlocked separate control knobs for direction (threading mode) and speed control (drilling mode) of the drill holder which ensures manipulation of the control knobs in a predetermined sequence.
2. Description of the Prior Art
In prior art drilling rigs, the drill holder is driven by a prime mover through a conventional power transmission system using non-modulatable friction type clutches. As a result, it is difficult to obtain smooth starting and stopping of the drill holder and the drill sometimes breaks. Furthermore, prior art control systems are not designed to guard against improper or injudicious use of the manually operable direction selection and speed regulation controls and, as a result, drills are more easily broken and other damage to the rig sometimes results.